BoilerFaultCodesThe 6 most common faults
01
A1 High Engineer
Your boiler is struggling because the internal water pump is stuck or cannot circulate water properly, preventing your heating and hot water from working.
Full guide for A102
A7 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the hot water it produces, so it has shut down to prevent overheating.
Full guide for A703
b1 High Engineer
Your boiler's internal computer is failing to communicate with its memory chip, causing the system to lock out for safety reasons.
Full guide for b104
C6 High Engineer
Your boiler is struggling to breathe because the internal fan is not spinning fast enough to safely clear exhaust gases, so it has safely shut itself down.
Full guide for C605
E2 High Engineer
Your boiler is struggling to read its own temperature because a component that monitors the heating water has stopped working correctly.
Full guide for E206
E9 High Engineer
Your boiler has detected that it is overheating and has automatically switched itself off to prevent damage to the system.
Full guide for E9on the Worcester Bosch CDi
Circulation pumpPump headHot water NTC sensorWiring harnessCode plugPrinted Circuit Board (PCB)
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Worcester Bosch shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue